Organic secondary batteries, which are rechargeable batteries that use an organic charge storage material as an electrode active material in the battery, are attracting considerable attention on account of such features as their high rate characteristics, high capacity retention with charge-discharge cycling, lightweight thin-film construction and potential physical flexibility. Nitroxyl radical-containing compounds are often used as the organic charge storage material (Chem. Phys. Lett. 359, 351-354 (2002); Electrochem. Soc. Interface 14, 32-36 (2005); JP-A 2002-117852), although the use of organosulfur polymers (J. Electrochem. Soc. 136, 661-664 (1989); Electrochimica Acta 46, 2305-2312 (2001)), quinone polymers (JP-A 2009-217992), quinoid materials (JP-A 2010-44882, JP-A 2010-55923, JP-A 2010-80343), dione materials (JP-A 2010-212152) and rubeanic acid-based materials (JP-A 2008-147015) has also been reported.
In recent years, it has been shown that, by using an organic charge storage material in the presence of an inorganic electrode active material, the capacity and voltage retention (collectively referred to below as the “rate characteristics”) during high-speed charge and discharge of a lithium ion battery and the capacity retention (referred to below as the “cycle characteristics”) in charge-discharge cycling can be improved (Scientific Reports 4, 4315-4321 (2014)), thus expanding applicable uses and methods for organic charge storage materials.